CS8900A datasheet(24/128 Pages) CIRRUS

24 / 128 page

DS271PP3

CS8900A

Crystal LAN™ ISA Ethernet Controller

CIRRUS LOGIC PRODUCT DATA SHEET

’C46 or ’CS46. If EEDI is high, the EEPROM is a

’C56, ’CS56, ’C66, or ’CS66.

3.4.7.2 Loading Configuration Data

The CS8900A reads in the first word from the EE-

PROM to determine if configuration data is con-

tained in the EEPROM. If configuration data is not

stored in the EEPROM, the CS8900A terminates

initialization from EEPROM and operates using its

default configuration (See Table 3). If configura-

tion data is stored in EEPROM, the CS8900A auto-

matically loads all configuration data stored in the

Reset Configuration Block into its internal Pack-

etPage registers.

3.4.8 EEPROM Read-out Completion

Once all the configuration data are transferred to

the appropriate PacketPage registers, the CS8900A

performs a checksum calculation to verify the Re-

set Configuration Blocks data are valid. If the re-

sulting total is 0, the read-out is considered valid.

Otherwise, the CS8900A initiates a partial reset to

restore the default configuration.

If the read-out is valid, the EEPROMOK bit (Reg-

ister 16, SelfST, bit A) is set. EEPROMOK is

cleared if a checksum error is detected. In this case,

the CS8900A performs a partial reset and is re-

stored to its default. Once initialization is complete

(configuration loaded from EEPROM or reset to

default configuration) the INITD bit is set (Register

16, SelfST, bit 7).

3.5 Programming the EEPROM

After initialization, the host can access the EE-

PROM through the CS8900A by writing one of

seven commands to the EEPROM Command regis-

ter (PacketPage base + 0040h). Figure 5 shows the

format of the EEPROM Command register.

3.5.1 EEPROM Commands

The seven commands used to access the EEPROM

are: Read, Write, Erase, Erase/Write Enable,

Erase/Write Disable, Erase-All, and Write-All.

They are described in Table 7.

3.5.2 EEPROM Command Execution

During the execution of a command, the two Op-

code bits, followed by the six bits of address (for a

’C46 or ’CS46) or eight bits of address (for a ’C56,

’CS56, ’C66 or ’CS66), are shifted out of the

CS8900A, into the EEPROM. If the command is a

Write, the data in the EEPROM Data register

(PacketPage base + 0042h) follows. If the com-

mand is a Read, the data in the specified EEPROM

ELSEL OP1 OP0

AD5 AD4

AD7 AD6

AD1 AD0

AD3 AD2

AD5 - AD0 used with

’C46 and ’CS46

AD7 - AD0 used with ’C56,

’CS56, ’C66 and ’CS66

Figure 5. EEPROM Command Register Format

Bit

Name

Description

[F:B]

Reserved

[A]

ELSEL

External Logic Select: When clear, the EECS pin is used to select the EEPROM.

When set, the ELCS pin is used to select the external LA decode circuit.

[9:8]

OP1, OP0

Opcode: Indicates what command is being executed (see next section).

[7:0]

AD7 to AD0

EEPROM Address: Address of EEPROM word being accessed.

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